FIG. 1 is a diagram illustrating a network structure of a universal mobile telecommunication system (UMTS). Generally, a UMTS system 10 comprises a user equipment (UE) 11, a UMTS terrestrial radio access network (UTRAN) 12, and a core network (CN) 13. Herein, the UE may be a mobile terminal in general. The UTRAN 12 comprises at least one of radio network sub-systems (RNSs) 13, and each RNS comprises a radio network controller (RNC) 131 and at least one of Node B 132 which is controlled by the RNC. The Node B includes at least one cell 133.
FIG. 2 is a diagram illustrating a layer structure of radio interface protocol in mobile communication system. As shown in FIG. 2, the radio interface protocol comprises horizontally a physical layer, a data link layer and a network layer. Meanwhile, the radio interface protocol comprises vertically a user plane for transmitting user data and a control plane for signaling.
The protocol layers of FIG. 2 comprises L1 (the first layer), L2 (the second layer) and L3 (the third layer). The layers of FIG. 2 correspond to 3 layers from the bottom according to the open system interconnection (OSI) layer structure.
The first layer, i.e., the physical (PHY) layer, provides the higher layer with information transfer service through physical channels. The PHY layer is connected to the second layer, i.e., medium access control (MAC) layer, with transport channels and data is transferred between MAC layer and PHY layer through the transport channels. Meanwhile, data is transferred between the PHY layers of a transmitting side and the PHY layer of a receiving side through the PHY channels.
The MAC layer provides a radio link control (RLC) layer with service through logical channels. The RLC layer of L2 supports reliable data transmission and may segment and concatenate service data units (SDUs) transferred from a higher layer.
A radio resource control (RRC) layer located at the bottom of L3 in the protocol layers is defined on the control plane, may control the logical channels, the transport channels and the physical channels in relation to configuration, reconfiguration and release of radio bearers (RBs). Herein, the RB means a service supported by L2 for data transmission between UE and UTRAN. Generally, to set up a RB means a process for defining a protocol layers and channels for providing a specific service, as well as a process for configuring parameters and operation, corresponding to the specific service.
Moreover, the RRC layer may broadcast system information through a broad control channel (BCCH). The system information regarding a cell is broadcasted to UEs using at least one of system information block (SIB). If the system information is modified, the UTRAN transmits BCCH modification information to the UEs through a paging channel (PCH) or a forward access channel (FACH), for the UEs to have the latest system information.
As an example of point-to-multipoint service, multimedia broadcast/multicast service (MBMS) is explained as follows. The MBMS supplies a streaming or background service using a MBMS bearer which is set up generally for downlink transmission. A MBMS service comprises at least one session, MBMS data is transmitted to UEs using the MBMS bearer during ongoing session. If the UE is activated corresponding to a service to which the UE have been subscribed, the UE may receive the service.
FIG. 3 is a diagram illustrating channels for MBMS. The UTRAN provides UEs with MBMS using a RB. The UTRAN may set up two types of RBs, i.e., a point-to-point RB and a point-to-multipoint RB. Herein, the point-to-point RB corresponds to a bi-directional RB. The point-to-point RB employs a dedicated traffic channel (DTCH) as a logical channel, a dedicated channel (DCH) as a transport channel, and a dedicated physical channel (DPCH) or a secondary common control physical channel (SCCPCH) as a physical channel.
Meanwhile, the point-to-multipoint RB corresponds to a uni-directional RB. As shown in FIG. 3, the point-to-multipoint RB may employ the MBMS traffic channel (MTCH) as a logical channel, the FACH as a transport channel, and the SCCPCH as a physical channel. The MTCH is configured for each MBMS provided in a cell, is used for transmission of user data corresponding to a MBMS on the user plane. A MBMS control channel (MCCH) which is a logical channel is mapped to the FACH, and the transport channel FACH is mapped to the SCCPCH. In general, one MCCH is allocated to one cell.
FIG. 4 is a diagram illustrating a method for transmitting MCCH information through the MCCH. As illustrated in FIG. 4, the MCCH information is transmitted through MCCH with two types of periods, i.e., modification period and repetition period. The MCCH information comprises critical information and non-critical information. The non-critical information may be modified in the modification period or in the repetition period. But, the critical information may be modified in the modification period. That is, the critical information is transmitted (repeatedly) during the modification period, and modified critical information is transmitted at the start time of the modification period. The MCCH information means a control message regarding MBMS, and the control message may be a RRC message. The MCCH information includes modified service information (MSI), unmodified service information (USI), point-to-multipoint RB information and access information. Herein, the access information message corresponds to the non-critical information, and the other information message corresponds to the critical information. The access information is transmitted per an access period which is equal to or less than the repetition period. Further, the repetition period may comprise multiple of the access period.
If the UTRAN transmits a control message corresponding to a MBMS, the control message includes a MBMS transmission identity. Herein, the MBMS transmission identity comprises a MBMS session identity and a MBMS service identity. For example, when the UTRAN transmits the MBMS MSI message, the MBMS MSI message includes the MBMS transmission identity and service information corresponding to the MBMS transmission identity.
The UTRAN periodically transmits information regarding whether the MCCH information is modified, thorough a MBMS notification Indicator channel (MICH). Therefore, if a UE wants to receive a specific MBMS data but a session of the specific MBMS doesn't start yet, the UE receives information through a MICH instead of a MCCH or a MTCH.
The UTRAN may modify the MCCH information by generating, adding, changing or deleting parameters from the MCCH information. The UTRAN transmits a MICH message and a MSI message to notify the UE of whether the MCCH information is going to be modified during the modification period. The MSI message includes at least one service identity corresponding to each service modified in the modification period, and information for operating the UE subscribed to the service. Herein, the service identity may be a MBMS transmission identity. The MBMS transmission identity may comprise a MBMS service identity identifying a service. Also, the MBMS transmission identity may comprise combination of a MBMS session identity and a MBMS service identity, the MBMS session identity identifies a service session. A service identity corresponding to a service not being modified during the modification period, among the services currently provided in a cell, is transmitted using a USI message. Herein, the service identity may be a MBMS transmission identity corresponding to the service.
When a service session of a MBMS starts, the UTRAN transmits, through the MICH, a notification indicator (NI) notifying UEs of receiving information through the MCCH. If a UE receives the NI from the UTRAN, the UE is trying to receive the MBMS data. If a UE receives a NI notifying the service modification through the MICH, the UE receives the MCCH information during the modification period indicated by the NI. During receiving the MCCH information, the UE receives the MSI message, and checks whether the MBMS is modified. If the UE detects modification of the MBMS, the UE receives modified MCCH information. Meanwhile, the UE receives the MSI and the USI messages which are transmitted during the modification period, and may acquire a service list listing all services currently provided in the cell in the modification period.
A UE trying to receive a MBMS service using a point-to-multipoint RB receives MCCH information including RB information through a MCCH, and sets up the point-to-multipoint RB in itself using the MCCH information. After setting up the point-to-multipoint RB, the UE receives MBMS data through the physical channel SCCPCH to which the logical channel MTCH is mapped.
The UTRAN may transmit the MBMS data through the MTCH. Herein, as illustrated FIG. 3, the UTRAN transmits a scheduling message to the UE through a MBMS scheduling channel (MSCH) corresponding to the SCCPCH to which the MTCH is mapped. The scheduling message includes information regarding a start point and an ending point of MBMS data transmission in a scheduling period. Therefore, the UTRAN informs the UE of a transmission period of scheduling information (scheduling period) in advance.
According to the related art, MCCH information is transmitted to UEs using the SIB through the BCCH. Therefore, if the MCCH is reconfigured, the UE receives BCCH modification information through the FACH or the PCH, and receives the SIB according to the BCCH modification information. Accordingly, the UE may acquire the MCCH reconfiguration information from the SIB. But, this process for acquiring the MCCH reconfiguration causes some problem. That is, in such case that the UE receives the BCCH reconfiguration information through the PCH, the reconfiguration of the MCCH may be delayed, because a discontinuous reception cycle (DTX cycle), i.e., a transmission period of the PCH, is longer than the MCCH modification period.